OBJECTIVE To determine whether an association exists between the histopathologic diagnosis of adenomyosis and infertility in a population of captive baboons. DESIGN Case-control study. SETTING Southwest National Primate Research Center. ANIMAL(S) Necropsy records of 37 baboons diagnosed with adenomyosis uteri and 38 baboons with normal uterine histology. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) Chi2 analysis of the association between adenomyosis, primary infertility, and the presence of coexisting endometriosis. RESULT(S) Endometriosis was associated with the presence of adenomyosis (OR = 31.5, 95% CI 4.2-1,348). There was a trend toward an association of endometriosis with the presence of lifelong infertility, but this correlation did not quite achieve statistical significance (OR = 3.6, 95% CI 0.9-15.8). Adenomyosis was associated with the presence of lifelong infertility (OR = 20.6, 95% CI 2.7-897). This association was maintained when cases of coexisting endometriosis (n = 17) were excluded (OR = 20.1, 95% CI 2.1-921). CONCLUSION(S) Adenomyosis is strongly associated with lifelong primary infertility in the baboon, even in the absence of coexisting endometriosis.